Marking is performed on a tire subjected to a performance test using a tire testing machine. In this marking, a heated marking pin presses a thermal transfer tape against the tire, so that a desired mark is printed on the tire by a thermal transfer method.
This marking is performed on a smooth surface of a side wall of the tire. However, the smooth surface decreases in area as the shape of the side wall becomes complicated in recent years. Further, the area of the smooth surface is small even in the side wall of the flat tire or the like. When the marking position is not smooth but uneven, the thermal transfer tape is sufficiently pressed against the convex portion, but the thermal transfer tape is not sufficiently pressed against the concave portion. As a result, the printing on the tire is not completely performed.
Therefore, Patent Document 1 discloses a marking head in which a bundle of needles are used as marking pins and the bundle of needles are inserted into a sheath using grease. In the marking head, the relative position between the needles changes so as to follow the uneven portion of the marking position. Thus, even when any uneven portion is present at the marking position, a desired mark is printed on the tire by the needles pressing the thermal transfer tape against the convex portion and the needles pressing the thermal transfer tape against the concave portion.
In the marking head of Patent Document 1, the adhesibility of grease is used to help the sheath to hold the bundle of needles. For this reason, when the marking pins are heated, the smooth grease is drooped and dropped from the needles to the tire, so that the tire or the mark is contaminated. Further, when the amount of grease inside the sheath decreases as the smooth grease is drooped and dropped, the needles slip out of the sheath, so that the complete printing may not be performed. In this way, in the marking head using grease, a problem arises in that the marking quality is degraded.